Biodegradable polyurethane/urea compositions

ABSTRACT

The present invention relates to biocompatible, biodegradable polyurethane/urea polymeric compositions that are capable of in-vivo curing with low heat generation to form materials suitable for use in scaffolds in tissue engineering applications such as bone and cartilage repair. The polymers are desirably flowable and injectable and can support living biological components to aid in the healing process. They may be cured ex-vivo for invasive surgical repair methods, or alternatively utilized for relatively non-invasive surgical repair methods such as by arthroscope. The invention also relates to prepolymers useful in the preparation of the polymeric compositions, and to methods of treatment of damaged tissue using the polymers of the invention.

FIELD OF THE INVENTION

The present invention relates to biocompatible, biodegradable polymericcompositions that are capable of in-vivo curing with low heat generationto form materials suitable for use in scaffolds in tissue engineeringapplications such as bone and cartilage repair. The polymers aredesirably flowable and injectable and can support living biologicalcomponents to aid in the healing process. They may be cured ex-vivo forinvasive surgical repair methods, or alternatively utilized forrelatively non-invasive surgical repair methods such as by arthroscope.The invention also relates to prepolymers useful in the preparation ofthe polymeric compositions, and to methods of treatment of damagedtissue using the polymers of the invention.

BACKGROUND

Biodegradable synthetic polymers offer a number of advantages over othermaterials in various biological applications including bone andcartilage repair. For example, in relation to the development ofscaffolds in tissue engineering, the key advantages include the abilityto tailor mechanical properties and degradation kinetics to suit variousapplications. Synthetic polymers are also attractive in tissueengineering applications because they can be fabricated into variousshapes with desired pore morphologic features conducive to tissue ingrowth. Furthermore, polymers can be designed with chemical functionalgroups that can, for example, induce tissue in-growth, or be utilised toadapt the polymers to the application in question.

A vast majority of biodegradable polymers studied belong to thepolyester family. Among these poly(a-hydroxy acids) such aspoly(glycolic acid), poly(lactic acid) and a range of their copolymershave historically comprised the bulk of published material onbiodegradable polyesters and has a long history of use as syntheticbiodegradable materials¹⁻³ in a number of clinical applications. Amongthese applications, poly(glycolic acid), poly(lactic acid) and theircopolymers, poly-p-dioxanone, and copolymers of trimethylene carbonateand glycolide have been the most widely used. The major applicationsinclude resorbable sutures, drug delivery systems and orthopedicfixation devices such as pins, rods and screws⁴⁻⁵. Among the families ofsynthetic polymers, the polyesters have been attractive for theseapplications because of their ease of degradation by hydrolysis of esterlinkage, degradation products are resorbed through the metabolicpathways in some cases and the potential to tailor the structure toalter degradation rates.

The recent interest in finding tissue-engineered solutions to repairdamaged tissues and organs due to injuries/diseases has made necessarythe development of new degradable polymers that meet a number ofdemanding requirements. These requirements range from the ability of thepolymer scaffold to provide mechanical support during tissue growth andgradually degrade to biocompatible products to more demandingrequirements such as the ability to incorporate cells, growth factorsetc and provide cell-conductive and inductive environments. Many of thecurrently available degradable polymers do not meet all of theserequirements. Furthermore, the development of in-situ polymerizablecompositions that can function as cell delivery systems in the form ofan injectable liquid/paste are becoming increasingly attractive intissue engineering applications.

Scaffolds made from synthetic and natural polymers, and ceramics havebeen investigated extensively for orthopedic repair⁶. This approach hasadvantages such as the ability to generate desired pore structures andthe ability to match size, shape and mechanical properties to suit avariety of applications. However, shaping these scaffolds to fitcavities or defects with complicated geometries, bonding to the bonetissues, and incorporating cells and growth factors, and therequirements of open surgery are a few major disadvantages of the use ofknown scaffold materials.

The synthetic polymers used in fabricating scaffolds for growing cellsbelong to the poly(ester family). For example, poly(glycolic acid) andpoly(lactic acid) have been the most commonly used polymers because oftheir relative ease of degradation under hydrolytic conditions and thedegradation products are resorbed to the body. However, these polymershave a number of disadvantages, including rapid loss of mechanicalproperties, difficulty in processing, and the acidity of degradationproducts resulting in tissue necrosis⁷.

Development of a degradable polymer composition that is ideally flowableand could be injected to fill a defect or cavity has number ofadvantages. A major advantage would be the possibility of administeringa gel arthroscopically in tissue engineering applications avoidingsurgery in many cases. Such a polymer would also have the advantage offilling cavities with complex geometries, and of providing good bondingto bone tissue. Incorporation of cells, growth factors and othercomponents to support cell growth could also be incorporated with a gel.Such polymer systems also have the potential to be formulated togenerate porous structure upon curing to facilitate nutrient flow tocells during growth and proliferation. Further, such systems may beuseful in pre-fabricating scaffolds with complex shapes havingappropriate pore structures with biological components alreadyincorporated.

Injectable polymer compositions based on ceramic and synthetic polymershave been reported. Ceramic materials such as calcium phosphate cementshave the disadvantage of very slow degradation, which in tissueengineering applications leads to decreased tissue regeneration at thesite of the implant, and poor mechanical properties⁶. To overcome someof these problems, injectable compositions based on poly(anhydrides) andpoly(propylene fumarate) have been developed. The general methodemployed includes the preparation of polymerisable precursors withhydrolyzable functional groups in the backbone and curing byfree-radical means using either chemical or photo initiation. Forexample, Mikos and coworkers⁸ have developed poly(propylene fumarate)based injectable systems by incorporating mineral fillers to improvemechanical strength. Similarly, Photo-cross-linkable poly(anhydrides)has also been developed for use in orthopedic applications, particularlyfocusing on achieving high mechanical strength. The systems developedare based on dimethacrylated anhydrides⁹. Both systems require highlevel of initiators as well as promoters to achieve short curing times.These polymer compositions generally have poor compressive strengths andoften require the incorporation of fillers to improve mechanicalstrength. Photo-curable systems also have the limitation of incompletecuring, particularly in thick samples due to poor light penetration.Further, the above polymer systems have limitations in terms of theoptions available for tailoring properties for different applications.

Over the last three decades the use of polyurethanes has been exploredin biomedical applications due to their excellent mechanical propertiesand great chemical versatility. Many years of research have resulted inthe development of biostable polyurethanes useful for a range oflong-term medical implants¹⁰.

Several research groups have reported on preparation and properties ofbiodegradable polyurethanes based on a range of polyester polyols. Bruinet al¹¹ reported on the synthesis of biodegradable poly(ester-urethae)elastomer networks by cross-linking star branched L-lactide andglycolide-ε-caprolactone copolymers with ethyl 2,6-diisocyanato hexane(LDI). Saad and coworkers¹²⁻¹³ reported biodegradable, elastic andhighly porous scaffolds based on poly (3-hydroxybutric acid) andpoly(caprolactone-co-diethylene glycol) polyols with aliphaticdiisocyanates. Bennett et al¹⁴ disclosed polymers useful for surgicaldevices, based on star polymers of soft segment forming monomers, whichcan be cross-linked with isocyanates.

Zang et al¹⁵ have described lysine diisocyanate, glycerol and waterbased biodegradable spongy polyurethanes that may be useful forbiomedical applications as suggested based on in-vitro test results.Story et al¹⁶⁻¹⁹ report on the preparation of hydrolysable poly(esternetworks) from L-lysine diisocyanate and D,L-lactide/ε-caprolactonehome—and copolyester triols and trimethylene carbonate homoployester andcopolyester triols. In these studies hydroxy functional polyester triolswere reacted with diisocyanates such as lysine diisocyanate and toluenediisocyanate to form network polyurethanes. Likewise, Bruin et al²⁰ havereported on biodegradable polyurethanes networks based on LDI andpoly(glycolide-co-ε-caprolactone) for fabrication of 2-layer artificialskin.

Spaans et al²¹⁻²³ discloses biomedical polyurethane-amides fromisocyanate-terminated polyester networks by reacting with dicarboxylicacid or hydroxycarboxylic acid in the presence of sodium chloridecrystals to produce macroporous structures suitable for repairingmeniscal lesion. Similarly, van Tienen et al²⁴ reported on thecaprolactone/L-lactide based polyurethane networks, fabricated to fromporous scaffolds useful for repair of knee meniscus defects.

Woodhouse et al²⁵ have disclosed a biodegradable polyurethane materialhaving a backbone containing at least one amino acid group suitable forwound dressings.

Notwithstanding the wide reporting of degradable polyurethanes in theliterature, there has been relatively little research directed to thedevelopment of degradable polyurethanes structurally tailored to bebiodegradable for tissue engineering. As a class of synthetic polymers,polyurethanes offer numerous opportunities to tailor materials withproperties and chemical composition to suit applications in soft tissueas well as hard tissue engineering applications. Several research papersdescribe polyurethanes with degradable polyester soft segments andmethods to fabricate porous scaffolds that support cell-growth. However,there are no reports on degradable polyurethane-based and desirablyinjectable polymer systems that can incorporate cells, growth factorsand other components to support cell growth as well or on curing suchpolymer compositions with low heat generation to minimize cell necrosis.

Accordingly, it is an object of the present invention to providebiodegradable, biocompatible polymers that are capable of supportingliving and non living biological additives during preparation and useand which are flowable, and preferably injectable. It is a furtherobject to provide prepolymer compositions that may be cured withdegradable oligomers ex vivo or in vivo to form the biocompatible,biodegradable polymers useful as scaffolds for tissue engineering.

These polymer prepared will desirably be capable of incorporatingbiological components such as cells, growth factors, and othercomponents such as nano-particle hydroxyapatite, calcium phosphate andother particles and can be cured in vivo or ex vivo to form solid,porous scaffolds for biomedical applications.

SUMMARY OF THE INVENTION

To this end there is provided star, dendrimer or hyper-branched flowableprepolymer composition comprising the reaction product of isocyanatesand low molecular weight multifunctional core molecules having at leasttwo and preferably three or more functional groups that react with saidisocyanates to form urethane or urea groups.

Throughout this specification, the term “core molecule” should be takento mean a molecule which has at least two, and preferably three or morefunctional groups that can react with isocyanate groups to form urethaneor urea groups.

Examples of core molecules include but are not limited to diols, triols,and polyols such as sugar molecules.

Preferably the core molecule has a molecular weight of 400 or less.

Isocyanates suitable for preparation of the flowable prepolymers of theinvention are those which are selected from the group consisting ofoptionally substituted aliphatic, aromatic and hindered isocyanates.Preferably the aliphatic isocyanates are asymmetric in molecular shapesince by being so, the rate of curing, and hence hardening of theprepolymer composition may be adjusted.

These prepolymer compositions, when introduced to functional oligomerswith degradable arms, may react in-vivo or ex-vivo to form porous ornon-porous cross-linked polymers which can be used as tissue engineeringscaffolds.

A “functional oligomer” according to the invention is a linear, star,dendrimer or hyperbranched oligomer.

Throughout this specification the term “comprises/comprising” when usedis taken to specify the presence of stated features, integers, steps orcomponents but does not preclude the presence or addition of one or moreother features, integers, steps, components or groups thereof.

It is surprisingly found that the prepolymer compositions according tothe invention have a viscosity which enables them to be utilised in aflowable form, and combined with a cross linker for delayed or slowcuring thus making them especially suited to biological applicationsincluding tissue engineering and repair. The prepolymer compositions canbe sterilized without risk to their physical and chemicalcharacteristics, preferably using gamma radiation to ensure sterility

Preferably the viscosity of the prepolymer composition on preparation isabout 15,000-200,000 cSt at room temperature.

Preferably the prepolymer composition may incorporate biological andinorganic components selected for their ability to aid tissue repair invivo, or to create certain physical characteristics in thebiocompatible, biodegradable polymer composition prepared from theprepolymer composition. These biological and inorganica components arepreferably selected from the group consisting of cells, progenitorcells, growth factors, other components for supporting cell growth,calcium phosphate, hydroxyapatite, nanoparticulate tricalcium phosphateand hydroxyapatite type fillers, adhesives including fibrin, collagenand transglutaminase systems, surfactants including siloxanesurfactants, silica particles, powdered silica, hollow fibres which maybe used to seed cells in the prepolymer composition, and other porogensincluding, for example, gelatin beads. The biological and inorganiccomponents may be present in quantities according to need, especially inthe case of the living additives such as cells and progenitor cells.Amounts of up to at least 20% w/w may be acceptable.

It is to be noted that a solvent is not essential to maintenance of theprepolymer composition at a viscosity suited to applications whereinflowability and preferably, injectability are desirable. This isespecially important in biological applications since many solvents arenot biocompatible and may, in fact, be toxic to cell sustainability.

The invention also provides a biodegradable biocompatiblepolyurethane/urea polymer composition comprising the reaction product ofprepolymers prepared according to the invention, and linear stardendrimer or hyperbranched soft segment forming functional oligomerswith degradable arms.

“Degradable arms” according to the invention are any molecular moietywhich may be part of the functional oligomers with which the prepolymercomposition is cross linked, which molecular moiety structure ispreferably biocompatible and bioresorbable on in-vivo degradation of thebiocompatible, biodegradable polyurethane/urea compositions.

The biocompatible, biodegradable polyurethane/urea compositions arepreferably flowable, more preferably injectable and cure with lowexotherm so as to make them particularly suited to supporting livebiological components. They may be cured ex-vivo and then implantedusing invasive medical procedures, or cured in-vivo, after insertion bynon-invasive medical methods such as by arthroscope. When cured, thepolyurethane/urea compositions according to the invention form abiodegradable biocompatible scaffold which may be porous and containinterpenetrating polymer networks so as to enable the inclusion ofbiological components such as cells, progenitor cells, growth factorsand other components for supporting cell growth. By selecting thecomponents of the prepolymer and the functional oligomers appropriately,the curing time of the biocompatible, biodegradable polyurethane/ureacompositions can be varied according to their application. The polymercompositions according to this aspect of the invention are referred tohereinafter as “biocompatible, biodegradable polyurethane/ureacompositions”.

The invention also provides a biodegradable, biocompatible polymericscaffold comprising a cured biocompatible, biodegradablepolyurethane/urea composition according to the invention.

Preferably the cured scaffolds according to this aspect of the inventionhave a compressive strength in the range of 0.05-80 MPa. The compressivestrength of the scaffold will vary according to its porosity andaccording to the biological components added.

Preferably the scaffolds have pores in the size range of 150-300 micron.More preferably these pores are formed from hollow fibres incorporatedin the prepolymer compositions employed in their production.

More preferably the porous scaffolds are seeded with living biologicalcomponents selected so as to aid the tissue repair process in thepatient being treated. The biological components so selected may becells, progenitor cells, growth factors and other components forsupporting cell growth. Suitable cells may include osteoblasts,chondrocytes, fibroblasts or other precursor cells.

In another aspect of the invention, there is provided a process for thepreparation of a biocompatible, biodegradable polyurethane/ureacomposition comprising

-   -   reacting an isocyanate with a core molecule having at least two        and preferably three or more functional groups that react with        said isocyanate to form urethane or urea groups under suitable        conditions to form a prepolymer with a flowable viscosity; and    -   reacting said prepolymer with a star soft segment forming        functional oligomer with degradable arms and optionally,        appropriate amounts of water and catalyst under conditions such        that the reaction temperature does not exceed 90° C., preferably        60° C. and more preferably 40° C.

Preferably the viscosity of the prepolymer formed is about15,000-200,000 cSt at room temperature.

Preferably, the process further comprises the step of adding biologicaland inorganic additives selected from the group consisting of cells,progenitor cells, growth factors, other components for supporting cellgrowth, calcium phosphate, hydroxyapatite, nanoparticulate tricalciumphosphate and hydroxyl apatite, adhesives including fibrin, collagen andtransglutaminase systems, surfactants including siloxane surfactants,silica particles, powdered silica, sugars, sodium chloride type salts,hollow fibres which may be used to seed cells in the prepolymercomposition, and other porogens including, for example, gelatin beads.More preferably this step is carried out in the formation of theprepolymer composition.

Preferably the process further comprises the step of reacting saidprepolymer with high molecular weight degradable polymer. The highmolecular weight degradable polymer may be selected from the groupconsisting of PLGA,PLLA and poly(anhydrides) and serves so as to assistin the establishment of interpenetrating networks of pores.

In another embodiment of the invention there is provided abiodegradable, biocompatible polyurethane/urea composition prepared by

-   -   reacting an isocyanate with a core molecule having at least two        and preferably three or more functional groups that react with        said isocyanate to form urethane or urea groups under suitable        conditions to form a flowable prepolymer; and    -   reacting said prepolymer with a star soft segment forming        functional oligomers with degradable arms and optionally,        appropriate amounts of water and catalyst under conditions such        that the reaction temperature does not exceed 90° C., preferably        60° C., more preferably 40° C.

Preferably the biocompatible, biodegradable polyurethane/ureacompositions so formed are utilizable as tissue engineering scaffolds.

Preferably the viscosity of the prepolymer formed is about15,000-200,000 cSt at room temperature.

The biocompatible, biodegradable polyurethane/urea compositions soformed are preferably porous.

Preferably the biocompatible, biodegradable polyurethane/ureacomposition further comprises biological additives selected from thegroup consisting of cells, progenitor cells, growth factors, othercomponents for supporting cell growth, calcium phosphate,hydroxyapatite, nanoparticulate tricalcium phosphate and hydroxyapatite,adhesives including fibrin, collagen and transglutaminase systems,surfactants including siloxane surfactants, silica particles, powderedsilica, sugars, sodium chloride type salts, hollow fibres which may beused to seed cells in the prepolymer composition, and other porogensincluding, for example, gelatin.

In these embodiments of the invention, it is surprisingly found thatwhereas in the prior art methods wherein a hard segment polymer isintroduced in a second polymerisation step, in the methods according tothe invention, the use of soft-segment polymers in the secondpolymerisation or cross linking step leads to low shrinkage in thesecond step due to the fact that fewer chemical bonds are needed toproduce a cross-linked polymer network. This is especially useful inbiological applications wherein a close fit between, for example, a bonecavity, and a temporary polymeric prosthesis is important.

A “hard segment” polymer according to the invention is one which imbuesthe copolymer with its physical strength which often arises from thealignment or formation of ordered domains of monomers of a common type.

A “soft segment” polymer according to the invention is typically formedfrom amorphous polyols with higher molecular weight than that of hardsegment forming compounds, and does not easily form ordered domains.

In another embodiment of the invention there is provided a method oftreatment of damaged bone or cartilage in a patient requiring suchtreatment, the method comprising administering to said patient abiocompatible, biodegradable polyurethane/urea composition according tothe invention, said administration occurring by the implant of ascaffold formed ex-vivo from a cured form of said polyurethane/ureacomposition, or by the injection of said polymer in an uncured form forin-vivo curing and scaffold formation. The composition may preferablyinclude biological additives to assist in the repair of the damaged boneor cartilage such as cells, progenitor cells, growth factors, or othersuitable materials. Biological additives used may preferably includeosteoblasts, chondrocytes, fibroblasts, fibrin, collagen,transglutaminase systems and the like.

The invention also provides for the use of biocompatible, biodegradablepolyurethane/urea compositions according to the invention as a tissueengineering scaffold for assistance in tissue engineering applicationssuch as bone and cartilage repair.

The biocompatible, biodegradable polyurethane/urea compositions may alsobe used in methods such as those described in WO 02/062357 (CSIRO andIndustrial Technology Research Institute) the contents of which areincorporated herein by cross reference.

Other embodiments of the invention will be evident from the followingdetailed description of various aspects of the invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the effect of water, lactose and triethylene glycol oncompressive strength on cured polymer scaffolds of the invention.

FIG. 2 shows an SEM photograph of a porous polymer scaffold according tothe invention.

FIG. 3 shows the effect of different degradable functional oligomers onthe average porosity of the cured polymer scaffolds of the invention.

FIG. 4 shows the effect of incorporating high molecular weightdegradable polymers and fillers on pore size and distribution in curedscaffolds of the invention.

FIG. 5 shows the effect of the incorporation of fillers on pore size anddistribution in cured polymer scaffolds of the invention.

FIG. 6 shows the effect of the incorporation of fillers on themechanical properties of cured polymer scaffolds of the invention.

FIG. 7 shows the porosity of cured polymer scaffolds according to theinvention incorporation hollow fibres.

FIG. 8 shows the effect of hydrolytic degradation on various polymerscaffolds according to the invention.

FIG. 9 shows the effect of hydrolytic degradation on polymer scaffoldsbased on phosphocholine modified polycaprolactone triol.

FIG. 10 shows the effect of oxidative degradation on a range of curedpolymer scaffolds according to the invention.

FIG. 11 shows an SEM photograph of a cured polymer scaffold preparedaccording to example 11.

FIG. 12 shows the change in polymer viscosity with curing time at 23° C.according to example 15.

FIG. 13 shows the temperature rise during polymer curing/gellingaccording to example 16.

FIG. 14 shows Haematoxylin and Eosin staining of a 6 week cultureshowing cluster of viable stem cells (purple) and new matrix (pink)within hollow fibres (transparent) within the polymer scaffold,according to example 31.

FIG. 15 shows a 6 week culture of human mesenchymal stem cells grown inhollow fibres within the polymer scaffold supplemented withdifferentiation medium to promote osteoblast differentiation accordingto example 31. Sample is stained with von Kossa to show bonemineralization (brown/black staining).

FIG. 16 shows Haemotoxylin and Eosin staining of a 4 week cultureshowing cluster of viable chondrocytes within resorbed gelatin beadswithin the polymer scaffold according to example 32.

FIG. 17 shows Alcian blue staining of a 9 week culture showing clusterof viable chondrocytes around gelatin beads within the polymer scaffoldaccording to example 32. Pink staining indicates cells and blue aroundcells indicates new glycosaminoglycan synthesis.

FIG. 18 shows micrographs showing cellular integration into the polymerstructure after 2 month implantation in rats (a) Polymer implant sample#1 (b) Polymer implant sample #2 according to example 34.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to star, dendrimer, and hyper-branchedprepolymers (referred to hereinafter as Prepolymer A) prepared from apreferably low molecular weight, multifunctional core-molecules andisocyanates. These prepolymers when reacted with functional oligomers,particularly star-shaped molecules with degradable arms (referred tohereinafter as Components B), may cross link in vivo or ex vivo to formporous or non-porous cross-linked polymers suitable for a variety oftissue engineering applications.

According to the present invention, a low molecular weight core moleculeis defined as one that has two, and preferably three or more functionalgroups that can react with isocyanate groups to from urethane or ureagroups. For example, pentaerythritol with four hydroxyl groups is asuitable core molecule. A range of other core molecules can be used andsome examples are

-   -   1. Glycerol    -   2. Pentaerythritol    -   3. Dipentaerythritol    -   4. Tripentaerythritol    -   5. 1,2,4-Butanetriol    -   6. Trimethylolpropane    -   7. 1,2,3-Trihydroxyhexane    -   8. Myo-inositol    -   9. Ascorbic acid    -   10. Glucose and isomers (D-galactose, D-mannose, D-fructose)    -   11. Maltose    -   12. Sucrose    -   13. Mannitol    -   14. N-Acetyl-D-glucosamine

Preferably the core molecule is a star, dendrimer or hyperbranchedmolecule having molecular weight of 400 or less. The higher themolecular weight of the core molecule selected the less likelihood thereis of the formation of a flowable, and preferably injectable prepolymercomposition.

Isocyanates suitable for preparing prepolymers according to the presentinvention are selected from the group consisting of optionallysubstituted aliphatic, aromatic and hindered isocyanates and arepreferably those with isocyanate groups having different reactivities,that is, those that are asymmetric. The optional substitution may occurin the alkyl of the ester group. Examples of such isocyanates include:

According to the present invention, the core molecule and excessisocyanate are preferably reacted without the presence of any solvent toform a star prepolymer. The quantities of the core molecule andisocyanate are stoichiometrically balanced with respect to the NOC andfunctional groups that can react with it. It is understood that commonsolvents such as DMF, THF, DMAc commonly used in polyurethane synthesismay be used in making the prepolymer A. However, in general, owing toissues with their biocompatibility, and due to the controlledflowability of the Prepolymer A, solvents will generally not berequired. Typical reactions involved are illustrated by example inScheme-1. Along with star polymers, dendritic and hyper-branchedprepolymers are formed during the reaction depending on the reactionconditions and the types of core molecules and isocyanates used.

The prepolymer (Prepolymer A) formation reaction may be catalyzed usinga range of known catalysts useful in making polyurethanes. Preferredcatalysts include stannous octoate, stannous 2-ethyl hexanoate,dibutyltin dilaurate, 1,4-diazabicyclo[2.2.2] octane, triethylamine, anddiaminoethanol. Other catalysts that may be useful include tetra n-butyltitanate, titanium acetylacetonate, triethanolamine titanate, titaniumethylaceto-acetate, tetraethyl titanate, tetraisopropyl titanate,titanium lactic acid chelate and other catalysts available under theTYZOR range from DuPont. Catalysis may or may not be utilised dependingon the period of time over which it is desired that Prepolymer A remainflowable and injectable. This will depend upon the environment in whichthe biocompatible, biodegradable polyurethane/urea composition is to beused, ex vivo or in vivo.

The prepolymer A is cured with component B to form biodegradable,biocompatible polyurethane/urea compositions which can be cured to formpolymer scaffolds.

Component B functional oligomers having degradable arms which may beused to cross-link the prepolymers of the invention may includelactides, glycolides, lactide/glycolides, caprolactones, propylenefumarates, glycolic acid, dioxanones, anhydrides, polyorthoesters andthe like. Functional oligomers which are zwitterionic can be desirablein circumstances where the resultant scaffolds are to be seeded withcells as they support cell growth. Functional oligomers formingcomponent B may be, but are not essentially, soluble in Prepolymer A. Inthe case that the functional oligomers B are soluble in Prepolymer A,this will aid delivery of the uncured, flowable biodegradable,biocompatible polyurethane/urea compositions of the invention, forexample, in some biomedical applications such as in arthroscopictreatments for bone replacement or temporary prosthesis. Particularlysuitable functional oligomers and degradable arms may include:

Other suitable functional oligomers and degradable arms includeethyleneglycol/lactides, polycaprolactone triols,dihydroxypolycaprolactones and other phosphoryl cholines.

The functional oligomer having degradable arms, Component B, isparticularly selected to import physical properties to cured polymercompositions of the invention.

The curing-cross linking reaction can be carried out under mildtemperature conditions. Typically, the reaction is preferably carriedout at temperatures ranging from 20° to 30° C. The catalystconcentration can be adjusted such that the temperature of the reactionmixture does not exceed 60° C. more preferably 40° C., and the mixturecan change from a viscous liquid to a putty like consistency in about 5to 45 min.

The mechanical properties of cured scaffolds according to the inventionare highly desirable. In particular, the cured scaffolds of theinvention have good compressive strength. FIG. 1 shows the effect ofwater, lactose and triethylene glycol on compressive strength of curedpolymer compositions of the invention. They can also be sterilizedusing, for example, gamma radiation, and will degrade in appropriatetime frames by oxidative or hydrolytic degradation.

The biological additives which may be incorporated in either prepolymerA or component B and injected in a tissue or bone repair site, usingsurgical or arthroscopic techniques may include but are not limited tocells, growth factors, progenitor cells, natural adhesives such asfibrin, collagen or transglutaminase system.

Inorganic fillers such as hydroxyapatite and tricalcium phosphate couldbe incorporated, preferably as nano-particles to reinforce the curedscaffold, and to support cell growth, particularly osteoblast andchondrocyte type cells, to either prepolymer A or component B. In apreferred embodiment, nano particles are incorporated in component B.The filler particles are dispersed in component B and mixed withprepolymer A to form rigid biodegradable, biocompatiblepolyurethane/urea compositions. It is speculated that nano-particleswill resorb faster, and accordingly may have an advantage over largerparticles.

Water may be added to component B to generate carbon-dioxide to provideporosity in the cured polymer. The amount of water may be controlleddepending on the desired pore size and content. Porosity can also begenerated by incorporating leachable compounds into either prepolymer Aor into the functional oligomer, or into the mixture of the twocomponents. Common porogens include salt and sugar crystals. Theseleachable compounds could be removed from the cross-linked polymer bysoaking in water, or by allowing them to slowly leach out in aqueousenvironments. It may also be possible to incorporate surfactantsincluding siloxane surfactants so that more water may be incorporatedthereby adjusting [pore size and distribution. Other porogens may beused including gelatin beads as described in WO 02/062357.

The biological components will be added in quantities suited to need,particularly in the case of cells, progenitor cells, fibrin, collagen,transglutaminase systems, and other living matter. Indicative amounts ofsome of the components are as follows. Calcium phosphate may bepreferably added in an amount of about 4%. Hydroxyapatite may be addedin an amount of about 5%. Collagen may be added in an amount of lessthan about 0.01%. Siloxane surfactant may be added in an amount of about5 mol %. Silica particles may be added in an amount of about 5%.

In trials conducted to date, porous scaffolds have been constructed andexamined under SEM. The results are shown in FIG. 2. The effects ofdifferent degradable functional oligomers were determined and theaverage porosity of the resultant average porosity measured. Theseresults are shown in FIG. 3.

The effect of incorporating degradable high molecular weight polymers incomponent B to form inter-penetrating networks has also beeninvestigated. These insertions enable the varying of degradation ratesof the cured polymer composition. PLGA, PLLA and polyanhydrides havebeen shown to be effective. FIG. 4 shows the effect of incorporatinghigh molecular weight degradable polymers and fillers on pore size anddistribution in cured scaffolds of the invention. FIG. 5 also shows theeffect of the incorporation of fillers on porosity. FIG. 6 shows theeffects of the incorporation of fillers of the mechanical properties ofcured scaffolds according to the invention.

Porous hollow fibres made from degradable polymers such as poly(lactide)poly(glycolide) and their copolymers, poly(anhydrides), and otherpolyesters, may be incorporated with or without cell seeding in thepreparation of prepolymer A or in component B. These hollow fibres formchannels to provide nutrients for cell growth and also can be used toseed cells and therefore prevent damage to them during the initialmixing process. FIG. 7 shows the porosity of cured polymers according tothe invention incorporating hollow fibres.

Preliminary degradation studies on cured scaffolds according to theinvention have been completed by in-vitro methods. Acceleratedhydrolysis (70° C. in PBS, pH 7.4) studies have been completed. FIG. 8shows the results of hydrolytic degradation on various polymersaccording to the invention.

One preferred cured biodegradable, biocompatible polyurethane/ureacomposition according to the invention uses as the functional oligomer(component B) phosphocholine modified polycaprolachone triol. Hydrolyticdegradation studies on these cured biodegradable, biocompatiblepolyurethane/urea compositions have been conducted and the results areshown in FIG. 9.

Oxidative degradation studies (70° C. in CoCl₂/H₂O₂) a range of curedbiodegradable, biocompatible polyurethane/urea compositions according tothe invention are shown in FIG. 10.

Examples 1 to 5 illustrate the preparation of prepolymer A according tothe present invention using a number of different core molecules.

Example 1

Materials: Pentaerythritol (Aldrich) was dried under vacuum (0.1 torr)at 80° C. over night. Methyl 2,6-diisocyanato hexanoate (MLDI, KyowaYuka Co., Ltd, Japan) and stannous 2-ethyl hexanoate (SEH, SigmaAldrich) were used as received. All the glassware used was thoroughlycleaned and dried at 105° C. overnight in an oven before use.

Predried pentaerythritol (4.818 g) was weighed in a dry three-neck flaskequipped with a magnetic stirrer, nitrogen inlet and drying tube. Methyl2,6-diisocyanato hexanoate (MLDI) (30.04 g) was then added to the flaskfollowed by catalyst stannous 2-ethyl hexanoate (0.1 wt %, 0.0348 g)under nitrogen. The reaction mixture was stirred and heated to 50° C.for 72 h under nitrogen atmosphere. The homogenous polymer mixture wasdegassed under vacuum (0.1 torr) at 50° C. before it was transferred toa vial under nitrogen atmosphere and stored in the refrigerator. Themolecular weight and viscosity of the prepolymer were determined by gelpermeation chromatography (GPC) and Bolin Rheometer, respectively.

GPO was performed on Water Associates Liquid Chromatograph system(Waters 717) equipped with a differential refractometer and fourp-Styragel columns (10⁵, 10⁴, 10³ and 100 Å). The mobile phase wastetrahydrofuran (THF) at a flow rate of 1 mL/min. Prepolymer wasdissolved in THF by warming the solution at 50° C. for 1 h and filteredthrough 0.45 micron filter before analysis. The system was calibratedwith narrow disperse polystyrene standards and molecular weights arereported as polystyrene equivalents.

The viscosity was measured using Bohlin Rheometer (CSR10) at 23° C.

The number average molecular weight and polydispersity of the prepolymerwere 1348 and 1.73, respectively based on GPC analysis. The prepolymerinstantaneous viscosity was 8.7×10⁴ cSt.

Example 2

Materials: Tripentaerythritol (Aldrich) was dried overnight under vacuum(0.1 torr) at 800C. MLDI and SEH were used as received.

Tripentaerythritol (6.98 g) was weighed in to a dry three-neck roundbottom flask equipped with a magnetic stirrer, nitrogen inlet and dryingtube. Methyl 2,6-diisocyanato hexanoate (31.81 g) was weighed separatelyand added to the flask followed by catalyst stannous 2-ethyl hexanoate(0.1 wt %, 0.038 g) under nitrogen. The reaction mixture was stirred andheated at 50° C. for 7 days under nitrogen atmosphere. The homogenouspolymer mixture was degassed under vacuum (0.1 torr) at the abovetemperature for about an hour before it was transferred to a vial undernitrogen atmosphere and stored in the refrigerator. Prepolymer wasanalysed for molecular weight and viscosity using the methods describedin Example 1.

The number average molecular weight and polydispersity of the prepolymerwere 827 and 1.36, respectively. The instantaneous viscosity was 3.2×10⁴cSt

Example 3

Materials: D-Glucose (Aldrich) was dried overnight in a vacuum oven (0.1torr) at 80° C. MLDI and stannous 2-ethyl hexanoate were used asreceived.

Predried D-Glucose (5.0 g) was weighed in to a dry three-neck roundbottom flask equipped with a magnetic stirrer, nitrogen inlet and dryingtube. Methyl 2,6-diisocyanato hexanoate (MLDI) (29.44 g) was thenweighed separately and added to the flask followed by catalyst stannous2-ethyl hexanoate (0.1 wt %, 0.0348 g) under nitrogen. The reactionmixture was stirred and heated at 50° C. for 72 h under nitrogenatmosphere. The homogenous polymer mixture with then degassed undervacuum (0.1 torr) at 50° C. before it was transferred to a vial undernitrogen atmosphere and stored in the refrigerator. The prepolymer wasanalysed by GPC and Rheometer (CLR-10) using methods described inExample 1.

The prepolymer number average molecular weight was 1430 and thepolydispersity was 1.75. Instantaneous viscosity was 1.5×10⁵ cSt at 23°C.

Example 4

Materials: Ascorbic acid (Aldrich) was dried overnight in a vacuum oven(0.1 torr) at 80° C. MLDI and stannous 2-ethyl hexanoate were used asreceived.

Predried ascorbic acid (5.15 g) was weighed in to a dry three-neck roundbottom flask equipped with a magnetic stirrer, nitrogen inlet and dryingtube. Methyl 2,6-diisocyanato hexanoate (24.57 g) was added to the flaskfollowed by catalyst stannous 2-ethyl hexanoate (0.1 wt %, 0.029 g)under nitrogen. The reaction mixture was stirred and heated to 50° C.for 9d under nitrogen atmosphere. The homogenous polymer mixture wasdegassed under vacuum (0.1 torr) at 50° C., transferred to a vial undernitrogen atmosphere and stored in the refrigerator. The prepolymer wasanalysed by GPC and Rheometer using methods described in Example 1.

The prepolymer number average molecular weight and polydispersity were672, and 1.12, respectively.

Example 5

Materials: Glycerol (Aldrich) was dried under vacuum (0.1 torr) forthree hours at 80° C. MLDI was used as received.

Predried Methyl 2,6-diisocynato hexanoate (41.47 g) was weighed in to adry three-neck round bottom flask equipped with a magnetic stirrer,nitrogen inlet and drying tube. Glycerol (6.0 g) was weighed separatelyand added drop wise to the flask at 70° C. and after the addition isover the reaction mixture was heated for 8 h under nitrogen. Theprepolymer was clear and homogeneous. The prepolymer was then degassedunder vacuum (0.1 torr), transferred to a vial under nitrogen atmosphereand stored in the refrigerator. The prepolymer was analysed by GPCaccording to the method described in Example 1.

The number average molecular weight of the prepolymer was 1541, whilethe polydispersity was 1.81.

Examples 6 to 8 illustrate the preparation of Prepolymer A usingdifferent diisocyanates.

Example 6

Materials: Pentaerythritol was dried as described in Example 1.Isophorone diisocyanate (IPDI, Aldrich) and stannous 2-ethyl hexanoatewere used as received.

Predried pentaerythritol (5.00 g) was weighed in to a dry-three neckflask equipped with a magnetic stirrer, nitrogen inlet and drying tube.Isophorone diisocyanate (IPDI) (32.65 g) was weighed separately andadded to the flask followed by catalyst stannous 2-ethyl hexanoate (0.1wt %, 0.037 g) under nitrogen. The reaction mixture was stirred andheated to 50° C. for 55 h under nitrogen atmosphere. The homogenouspolymer mixture was degassed under vacuum (0.1 torr) at 50° C.,transferred to a vial under nitrogen atmosphere and stored in therefrigerator. The prepolymer was analysed by GPC using the methoddescribed in Example 1.

The prepolymer number average molecular weight was 1407 andpolydispersity 1.21.

Example 7

Materials: Pentaerythritol was dried as described in Example 1.Hexamethylene diisocyanate (HDI, Aldrich) and stannous 2-ethyl hexanoatewere used as received.

Predried pentaerythritol (5.00 g) was weighed in to a dry three-neckround bottom flask equipped with a magnetic stirrer, nitrogen inlet anddrying tube. Hexamethylene diisocyanate (24.71 g) was then weighedseparately and added to the flask followed by catalyst stannous 2-ethylhexanoate (0.029 g, 0.1 wt %,) under nitrogen. The reaction mixture wasstirred and heated to 50° C. for 72 h under nitrogen atmosphere. Thehomogenous polymer mixture was then degassed under vacuum (0.1 torr) at50° C., transferred to a vial under nitrogen atmosphere and stored inthe refrigerator. The prepolymer was analysed by GPC using the methoddescribed in Example 1.

The number average molecular weight and polydispersity of the prepolymerwere 1083 and 1.52, respectively.

Example 8

Materials: D-Glucose was dried as described in Example 3. Ethyl2,6-diisocyanato hexanoate (ELDI, Kyowa Yuka Co., Ltd, Japan) andstannous 2-ethyl hexanoate were used as received.

Predried D-Glucose (5.0 g) was weighed in to a dry three-neck roundbottom flask equipped with a magnetic stirrer, nitrogen inlet and dryingtube. Ethyl 2,6-diisocyanato hexanoate (Ethyl-LDI) (31.38 g) was weighedseparately and added to the flask followed by stannous 2-ethyl hexanoate(0.1 wt %, 0.036 g) under nitrogen. The reaction mixture was stirred andheated to 50° C. for 72 h under nitrogen atmosphere. The homogenouspolymer mixture was then degassed under vacuum (0.1 torr) at the abovetemperature and was transferred to a vial under nitrogen atmosphere andstored in the refrigerator. The prepolymer was analysed by GPC using themethod described in Example 1.

Prepolymer GPC analysis showed a number average molecular weight of 1510and polydispersity of 2.5. Instantaneous viscosity was 2.6×10⁴ cSt at23° C.

Example 9

This example illustrates the preparation of prepolymer without the useof a catalyst.

Materials: D-Glucose (Aldrich) was dried overnight in a vacuum oven (0.1torr) at 80° C. Methyl 2,6-diisocyanato hexanoate (MLDI) was used asreceived.

Predried D-Glucose (5.0 g) was weighed in to a dry three-neck roundbottom flask equipped with a magnetic stirrer, nitrogen inlet and dryingtube. MLDI (29.44 g) was then weighed and added to the flask. Thereaction mixture was stirred and heated at 100° C. for 6d under nitrogenatmosphere. The homogenous polymer mixture was degassed under vacuum(0.1 torr) at the above temperature, transferred to a vial undernitrogen atmosphere and stored in the refrigerator. The prepolymer wasanalysed by GPC and Rheometer (CSR-10).

The prepolymer number average molecular weight was 1333 and thepolydispersity 1.81. Instantaneous viscosity was 1.2×10⁵ cSt at 23° C.

Example 10

Materials: Pentaerythritol tetrakis (3-mercaptopropionate) (PETMP,Aldrich) was dried under vacuum (0.1 torr) at 90° C. for three hours.MLDI was used as received.

Predried PETMP (10.0 g) was weighed in to a dry three-neck round bottomflask equipped with a magnetic stirrer, nitrogen inlet and drying tube.Methyl 2,6-diisocynato hexanoate (MLDI) (17.37 g) was then weighedseparately and added to the flask. The reaction mixture was stirred andheated at 70° C. for 72 h under nitrogen atmosphere. The homogenouspolymer mixture was then degassed under vacuum (0.1 torr) at the abovetemperature before it was transferred to a vial under nitrogenatmosphere and stored in the refrigerator. The prepolymer was analysedby GPC and Rheometer (CSR-10) using methods described in Example 1.

The prepolymer number average molecular weight was 1564 and thepolydispersity was 1.94. Instantaneous viscosity was 7.5×10⁴ cSt at 23°C.

Examples 11-14 illustrate the preparation of porous and non-porouspolymers using the prepolymer prepared in Example 1.

Example 11

Materials: Prepolymer of MLDI and pentaerythritol was prepared accordingto Example 1. Polycaprolactone triol (MW 300, PCLT-300, Aldrich) wasdried by heating under vacuum (0.1 torr) at 90° C. for three hours.

Degassed prepolymer (2.20 g) prepared in Example 1 was weighed into acavity (20×20×10 mm) made in a Teflon block. Degassed and driedpolycaprolactone triol (MW 300, 0.80 g) was added to this prepolymerfollowed by water (0.008 g). The mixture was stirred for few seconds andthen stannous 2-ethyl hexanoate catalyst (0.003 g, 0.1%) was added andstirred further for 5 min. This prepolymer mixture remained a viscousliquid and was taken into a 2.5 ml syringe and dispensed 0.29 g to eachof the cylindrical (6 D×12 H mm size) cavities in a Teflon mould, sealedand cured overnight at 38° C. to give porous cylindrical test specimens.The cured polymer samples were tested using Instron (Model 5568) forcompressive strength and modulus according to ASTM method F451-95.

The average compressive strength and modulus were 22.2±4.6 MPa and613±138 MPa, respectively.

A sample of the cured polymer was examined by Scanning ElectronMicroscopy to evaluate the polymer porosity. A representative micrographis shown in FIG. 11 which illustrates that the cured polymer sample isporous.

Example 12

Materials: Prepolymer of MLDI and pentaerythritol was prepared accordingto Example 1. Polycaprolactone triol (MW 300, PCLT-300, Aldrich) wasdried by heating under vacuum (0.1 torr) at 90° C. for three hours.Nanoparticles (50-100 nm) of hydroxyapatite (Aldrich) was incorporatedinto PCL-300 by dispersion method Degassed prepolymer (1.13 g) preparedin Example 1 was weighed in to a cavity (20×20×10 mm) made in a Teflonblock. Degassed and dried polycaprolactone triol containing 5 wt %nanoparticles of hydroxyapatite (MW 300, 0.41 g) was added to thisprepolymer followed by water (0.004 g). The mixture was stirred using aspatula for few seconds and then stannous 2-ethyl hexanoate catalyst(0.0015 g, 0.1%) was added and stirred further for few min. Thisprepolymer mixture remained a viscous liquid and was taken into a 2.5 mlsyringe and dispensed 0.29 g to each of the cylindrical (6 D×12 H mmsize) cavities in a Teflon mould, sealed and cured overnight at 38° C.to give porous cylindrical test specimens. The cured polymer sampleswere tested using Instron (Model 5568) for compressive strength andmodulus according to ASTM method F451-95.

The average compressive strength and modulus were 14.4±3 MPa and 512±115MPa, respectively.

Example 13

Materials: Prepolymer of MLDI and pentaerythritol was prepared accordingto Example 1. Polycaprolactone triol (MW 300, PCLT-300, Aldrich) wasdried by heating under vacuum (0.1 torr) at 90° C. for three hours.Lactose was dried overnight under vacuum (0.1 torr) at 80° C.

Degassed prepolymer (1.24 g) prepared in Example 1 was weighed in to acavity (20×20×10 mm) made in a Teflon block. Degassed and driedpolycaprolactone triol (0.32 g) and Lactose (0.056 g) water (0.0045 g).The mixture was manually stirred for a few seconds and then stannous2-ethyl hexanoate catalyst (0.0016 g, 0.1%) was added and stirredfurther for few minutes. This prepolymer mixture remained a viscousliquid and was taken into a 2.5 ml syringe and dispensed 0.29 g to eachof the cylindrical (6 D×12 H mm size) cavities in a Teflon mould andcured overnight at 38° C. to give porous cylindrical test specimens. Thecured polymer samples were tested using Instron (Model 5568) forcompressive strength and modulus according to ASTM method F451-95.

The average compressive strength and modulus were 16.6±4 MPa and 536±122MPa, respectively.

Example 14

Degassed prepolymer (3.61 g) of pentaerythritol and MLDI prepared inExample 1 was weighed in to a cavity (2×2×1 cm) made in a Teflon block.Degassed polycaprolactone triol of molecular weight MW 300 (1.46 g) wasadded to prepolymer followed by 0.1 wt % of 2-ethyl hexanoate catalyst.The polymer mixture was stirred for few minutes manually using aspatula. The viscous polymer was taken into a 2.5 ml syringe anddispensed 0.45 g into each cylindrical cavity (6 mm D×12 mm L) in amulti-cavity Teflon mould and cured overnight at 38° C. to givenon-porous cylindrical polymer test specimens.

The cured polymer samples were tested using Instron (Model 5568) forcompressive strength and modulus according to ASTM method F451-95.

The polymer samples exhibited 61.9±5.3 MPa, and 837±216 MPa averagecompressive strength and modulus, respectively.

Example 15

Materials: Prepolymer of MLDI and pentaerythritol was prepared accordingto Example 1. Polycaprolactone triol (MW 300, PCLT-300, Aldrich) wasdried by heating under vacuum (0.1 torr) at 90° C. for three hours.Prepolymer was degassed under vacuum (0.1 torr) at 50° C. for 20 minwith stirring.

Degassed prepolymer (1.0 g) based on pentaerythritol and MLDI preparedaccording to Example 1 was weighed separately into two cavities(20×20×10 mm) made in Teflon blocks. Dried polycaprolactone triol (MW300, 0.406 g) was added to prepolymer in one cavity and the mixture wasstirred for a few seconds. Catalyst stannous 2-ethyl hexanoate (0.1%based on total weight of prepolymer A and PCLT) was added and stirred.The viscosity of the reaction mixture was monitored using a Rheometer(CLR-10) at 23° C. FIG. 2 illustrates the change in viscosity over thatperiod. Similarly, the second sample was prepared by adding driedpolycaprolactone triol (MW 300, 0.406 g) and stannous 2-ethyl hexanoate(0.8% based on total weight of prepolymer A and PCLT) and the viscositywas monitored using the Rheometer. The reaction gel time in the secondsample was significantly shorter as illustrated by the higher viscosityshown in FIG. 2.

Example 13 to 16 illustrate the preparation of polymers based on a rangeof commercially available as well as laboratory synthesized polyols(prepolymer B) and their mixtures as well as the preparation of polymerswith additives such as nanoparticle fillers for improvement ofmechanical strength.

Example 16

Materials: Prepolymer of MLDI and pentaerythritol was prepared accordingto Example 1. Polycaprolactone triol (MW 300, PCLT-300, Aldrich) wasdried by heating under vacuum (0.1 torr) at 90° C. for three hours.Prepolymer was degassed under vacuum (0.1 torr) at 50° C. for 20 minunder stirring.

Degassed prepolymer (0.564 g) of pentaerythritol and MLDI prepared inExample 1 was weighed in to a cavity (20×20×10 mm) made in a Teflonblock. Polycaprolactone triol (MW 300, 0.206 g) was added to thisprepolymer followed by water (0.002 g). The mixture was stirred for fewseconds and then stannous 2-ethyl hexanoate catalyst (0.0046 g, 0.6%based on total weight of prepolymer, PCLT and water) was added andstirred with a thermocouple probe dipped into the reaction mixture tomonitor the reaction temperature. The catalyst concentration in thisexperiment was adjusted to achieve fast reaction and short gel time. Themaximum temperature reached was 40° C. as shown by the temperatureprofile in FIG. 13.

Example 17

Materials: Prepolymer prepared in Example 1 was used in this experiment.Polycaprolactone triol (MW 300, PCLT-300, Aldrich) was dried by heatingunder vacuum (0.1 torr) at 90° C. for three hours. Prepolymer wasdegassed under vacuum 0.1 torr at 50° C. for 20 min under stirring.

A polyol based on ethylene glycol and lactide (EG:Lactide) was preparedaccording to the following procedure.

Recrystallised lactide (5.77 g, MW 144, 0.0401 mol) and ethylene glycol(131.73 g, MW 62.02, 2.12 mol) were placed in a dry 500 mL round bottomflask fitted with a suba seal, condenser and nitrogen inlet. The flaskwas purged with nitrogen overnight and then heated to 90° C. for 1 h inan oil bath. The reaction temperature was raised to 135° C. and heatedfor further 3 days. The reaction was cooled down to 55° C. and excessethylene glycol was completely removed at 55° C. under vacuum (0.02torr) to yield a colourless liquid. ¹H and ¹³C NMR supported thestructure of the product.

(Ref: Makromol. Chem., 193, 1623-1631, 1992 J. of Polym. Science: PartA: Polymer Chemistry, Vol. 39, 973-985, 2001. and Macromol. Chem. Phys.201, 11, 1067-1076, 2000.)

Degassed prepolymer (2.17 g) of pentaerythritol with MLDI prepared inExample 1 was weighed in to a cavity (20×20×10 mm) made in a Teflonblock. Degassed and dried polycaprolactone triol of molecular weight (MW300, 0.572 g) and EG:lactide polyol (MW 134, 0.147 g) were added to thisprepolymer followed by water (0.008 g). The mixture was stirred for afew seconds and then stannous 2-ethyl hexanoate catalyst (0.0028 g, 0.1wt % of based on total weight of prepolymer, PCLT and water) was addedand stirred further for 5 min. The mixture which was a viscous andinjectable liquid was then taken into a 2.5 ml syringe and dispensed0.45 g samples into each cylindrical cavity (6 mm D×12 mm H) in amulti-cavity Teflon mould, sealed and cured overnight at 38° C. to giveporous cylindrical polymer test specimens.

The cured polymer samples were tested using Instron (Model 5568) forcompressive strength and modulus according to ASTM method F451-95.

The polymer samples exhibited 12.8±4.1 mpa, and 393±47 MPa averagecompressive strength and modulus, respectively.

Example 18

Materials: Prepolymer prepared in Example 1 was used in this experiment.Polycaprolactone diol (MW 1000, PCLD-1000, Aldrich) was dried by heatingunder vacuum (0.1 torr) at 90° C. for three hours. Prepolymer wasdegassed under a vacuum (0.1 torr) at 50° C. for 20 minuets withstirring.

Degassed prepolymer (1.40 g) of pentaerythritol with MLDI prepared inExample 1 was weighed in to a cavity (20×20×10 mm) made in a Teflonblock. Degassed and dried polycaprolactone diol of molecular weight (MW1000, 2.57 g) and water (0.005 g) was added to the prepolymer. Themixture was stirred for few seconds and then stannous 2-ethyl hexanoatecatalyst (0.004 g, 0.1% based on based on total weight of prepolymer,PCLD and water) was added and stirred further for 5 min. The mixturewhich was a viscous and injectable liquid, was taken into a 2.5 mlsyringe and dispensed 0.29 g into each cylindrical cavity(6 mm D×12 mmL) in a multi-cavity Teflon mould, sealed and cured overnight at 38° C.to give porous cylindrical polymer test specimens.

The cured polymer samples were tested using Instron (Model 5568) forcompressive strength and modulus according to ASTM method F451-95.

The polymer samples exhibited 1.5±0.8 MPa, and 2.7±1.0 MPa averagecompressive strength and modulus, respectively.

Example 19

Materials: Prepolymer prepared in Example 8 was used in this experiment.Polycaprolactone triol (MW 300, Aldrich) was dried by heating undervacuum (0.1 torr) at 90° C. for three hours.

Degassed prepolymer (2.27 g) of D-glucose with ELDI prepared in Example8 was weighed in to a cavity (2×2×1 cm) made in a Teflon block. Degassedand dried polycaprolactone triol of molecular weight (MW 300, 0.77 g)and water (0.007 g) was added to the prepolymer. The mixture was stirredfor few seconds and then 0.1 wt % of stannous 2-ethyl hexanoate catalyst(0.003 g, 0.1% based on based on total weight of prepolymer, PCLT andwater) was added and stirred further for 5 min. The mixture which was aviscous and injectable liquid was taken into a 2.5 ml syringe anddispensed 0.29 g into each cylindrical cavity (6 mm D×12 mm H) in amulti-cavity Teflon mould, sealed and cured overnight at 38° C. to giveporous cylindrical polymer test specimens.

The cured polymer samples were tested using Instron (Model 5568) forcompressive strength and modulus according to ASTM method F451-95. Thepolymer samples exhibited 8.6±0.4 MPa, and 109±11 MPa averagecompressive strength and modulus, respectively.

Example 20 describes the method of preparing prepolymersdihydroxypolycaprolactone phosphoryl choline (DPCLPC) and synthesis ofdihydroxyglycerol phosphoryl choline (DGPC).

Example 20

Dihydroxypolycaprolactone phosphoryl choline (DPCLPC) was prepared usinga modified literature reported procedure (Ref; Polymer J, 22, p 355-360,(1990).

Predried polycaprolactone-300 (17.98 g, 0.0599 mol), triethylamine(6.049 g, 0.0599 mol) and dry THF (150 ml) were placed in a 500 mlthree-neck round bottom flask fitted with suba seal, dropping funnel andnitrogen inlet. The solution was cooled to −30° C. and 8.5363 g (0.0599mol) 2-chloro-2-oxo-1,3,2-dioxaphospholane (COP) dissolved in smallamount THF was added slowly via syringe to the solution. The temperatureof the reaction was maintained at −30° C. during addition (about 1 hour)and maintained that temperature for two more hours. The reaction mixturewas slowly warmed to 10° C. and filtered carefully using a Buchnerfunnel under reduced pressure. The filtrate was evaporated under reducedpressure to yield a clear viscous liquid. Yield of2-(2-oxo-1,3,2-dioxaphospholoxy)polycaprolactone diol was 23.74 g.

2-(2-oxo-1,3,2-dioxaphospholoxy)polycaprolactone diol (23.74 g, 0.0537mol) was placed in a 250 ml glass-pressure bottle with dry acetonitrile(135 mL). The glass bottle was cooled to −30° C. and anhydroustrimethylamine (3.54 mL) was rapidly added to the solution and thepressure bottle was closed and heated to 55° C. with stirring for 3days. The product was transferred to 100 mL round bottom flask undernitrogen and dried under reduced pressure to yield a slight yellowviscous product. Yield 29 g. The IR and ¹H NMR confirmed the structureof dihydroxypolycaprolactone phosphoryl choline (DPCLPC).

Dihydroxyglycerol phosphoryl choline (DGPC) was prepared according tothe literature reported method (Polym. J. 22, 5, 355-360, 1990, andAustralian Journal of Chemistry, 55, 629-634, 2002.

In this case, hydroxyl groups were protected before introducingphosphorylcholine arms using the above described method and subsequentlydeprotected to yield dihydroxyglycerol phosphoryl choline (DGPC).

Example 21

Materials: Prepolymer of MLDI and pentaerythritol was prepared accordingto Example 1. Polycaprolactone triol (MW 300, PCLT-300, Aldrich) wasdried by heating under vacuum (0.1 torr) at 90° C. for three hours.Dihydroxypolycaprolactone phosphoryl choline (DPCLPC) was preparedaccording to the method described in Example 20.

Degassed prepolymer (1.24 g) of Pentaerythritol with MLDI prepared inExample 1 was weighed in to a cavity (20×20×10 mm) made in a Teflonblock. Degassed and dried polycaprolactone triol (MW 300, 0.353 g) andDPCLPC (MW 501.4, 0.252 g) was added to this prepolymer followed bywater (0.0045 g). The mixture was stirred for a few seconds and thenstannous 2-ethyl hexanoate catalyst (0.1-wt % based on total weight ofprepolymer, DPCLPC, PCLT and water) was added and stirred further for 5min. The viscous polymer was then taken into a 2.5 ml syringe anddispensed 0.24 g into each cylindrical cavity (6 mm D×12 mm H) in amulti-cavity Teflon mould and cured overnight at 38° C. to give porouscylindrical polymer test specimens.

The cured polymer samples were tested using Instron (Model 5568) forcompressive strength and modulus according to ASTM method F451-95.

The average compressive strength and modulus of the polymer were 9.4±1.6MPa and 390±1 MPa, respectively.

Example 22

Materials: Prepolymer of MLDI and D-glucose was prepared according toexample 3. Prepolymer was degassed under vacuum (0.1 torr) at 50° C. for20 minuets under stirring dihydroxypolycaprolactone phosphoryl choline(DPCLPC) was prepared was prepared according to the method described inExample 15. DPCLPC was dried and degassed by heating under vacuum (0.1torr) at (90° C.) for three hours.

Degassed prepolymer (2.50 g) of D-Glucose with MLDI prepared in Example3 was weighed in to a cavity (2×2×1 cm) made in a Teflon block. Degassedand dried DPCLPC (MW 501.4, 2.52 g) was added to this prepolymer. Themixture was stirred for a few seconds and then 0.1 wt % of stannous2-ethyl hexanoate catalyst (0.005 g) was added. Gelatine beads (0.3 mLin water, 100-200 micron size) was added to this mixture and stirred forabout 1 minute. The viscous polymer was then taken into a 2.5 ml syringeand dispensed (0.29 g) into each cylindrical cavity (6 mm D×12 mm H) ina multi-cavity Teflon mould and cured overnight at 38° C. to give porouscylindrical polymer test specimens.

The cured polymer samples were tested using Instron (Model 5568) forcompressive strength and modulus according to ASTM method F451-95.

The average compressive strength and modulus of the polymer were0.05±0.1 MPa and 0.18±0.03 MPa, respectively.

Example 23

Materials: Prepolymer of MLDI and D-glucose was prepared according toexample 3. Polycaprolactone triol (MW 300, PCLT-300, Aldrich) was driedby heating under vacuum (0.1 torr) at 90° C. for three hours. Prepolymerwas degassed under vacuum (0.1 torr) at 50° C. for 20 min whilestirring. Dihydroxypolycaprolactone phosphoryl choline (DPCLPC) wasprepared according to the method described in Example 15.

Degassed prepolymer (2.50 g) of D-Glucose with MLDI prepared in Example3 was weighed in to a cavity (20×20×10 cm) made in a Teflon block.Degassed and dried polycaprolactone triol (MW 300, 0.906 g) and DPCLPC(MW 501.4, 0.252 g) was added to the prepolymer. The mixture wasmanually stirred using a spatula for few seconds and then stannous2-ethyl hexanoate catalyst (0.0036 g) was added and stirred for 20 min.Gelatine (0.3 mL, ave. size 100-200 micron, in water) was added to thismixture and stirred for about 1 minute. The viscous polymer was thentaken into a 2.5 ml syringe and dispensed 0.29 g into each cylindricalcavity (6 mm D×12 mm H) in a multi-cavity Teflon mould and curedovernight at 38° C. to give porous cylindrical polymer test specimens.

The cured polymer samples were tested using Instron (Model 5568) forcompressive strength and modulus according to ASTM method F451-95.

The compressive strength of the polymer was 0.3±0.2 MPa and compressivemodulus of 2.9±0.9 MPa.

Example 24

Materials: Prepolymer of MLDI and D-glucose was prepared according toexample 3. Polycaprolactone triol (MW 300, PCLT-300, Aldrich) was driedby heating under vacuum (0.1 torr) at 90° C. for three hours.

1,2-Dihydroxy-N,N-dimethylaminopropane sulfonate (DDAPS) zwitterion wasprepared using a procedure adopted from a method previously reported(Ref: Industrial and Engineering Chemistry, Vol 56, 41-45, Fischer,1954).

The following is a brief description of the method used.

Propane diol (9.88 g, 0.082 mol) was weighed into a three neck flaskequipped with a drying tube and nitrogen inlet. Methanol (20 ml) addedto this under nitrogen and stirred until dissolved. 1,3-propane sultone(10.1 g, 0.082 mol) was added slowly with stirring at room temperature.The reaction was stirred for about 2 h, until DDAPS zwitterionprecipitates out. The zwitterion was filtered and washed with coldmethanol and dried under vacuum at 70° C. to yield an amorphous powder.The ¹H NMR supported the structure of1,2-dihdroxy-N,N-dimethylamino-propane sulfonate. Yield 12.57 g.

Degassed prepolymer (2.06 g) of D-Glucose with MLDI prepared in Example3 was weighed in to a cavity (20×20×10 cm) made in a Teflon block.Degassed and dried polycaprolactone triol (MW 300, 0.66 g) and DDAPS (MW241.16, 0.1 g) was added to the prepolymer followed by water (0.007 g).The mixture was stirred for few seconds and then stannous 2-ethylhexanoate catalyst (0.0028 g) based was added and stirred for fewminutes. The viscous polymer was then taken into a 2.5 ml syringe anddispensed (0.29 g) into each cylindrical cavity (6 mm D×12 mm L) in amulti-cavity Teflon mould and cured overnight at 38° C. to give porouscylindrical polymer test specimens.

The cured polymer samples were tested using Instron (Model 5568) forcompressive strength and modulus according to ASTM method F451-95.

The compressive strength of the polymer was 7.1±0.8 MPa and compressivemodulus of 80.2±14 MPa.

Example 25

The prepolymer prepared in examples 1, 2 and 3 and the cured polymersmade by mixing prepolymer 1 with polycaprolactone triol, EG:lactide andhydroxyapatite as illustrated in examples 11, 12, 13 and 16,respectively were evaluated for their cytotoxicity against human and ratstem cells. The test protocol described in International Organisationfor Standardisation Guidelines as stated in ISO 10993-5 (Biologicalevaluation of medical devices) was used.

Tests for cytotoxicity to determine the biological response of mammaliancells in vitro were developed to look at a) extracts of the device, b)in contact with the device.

Cells used were stem cells from either human and rat origin.

In most cases a negative and positive control for cytotoxicity and areagent control were used. Culture vessels were of tissue culture grade(TCP), thus providing a good -ve cytotoxic control. Cells were used at80% confluence to ensure cells were in logarithmic growth phase. Cellswere maintained in test conditions overnight (24 hrs) at 37° C. beforemeasuring cytotoxicity with a reagent (MTS), which is only convertedwith metabolically active cells.

Liquid monomers/prepolymers were tested on pre-seeded cells, added witha culture medium change, and left on cells for 24 hrs, before removingculture medium and adding MTS reagent, incubating for a further 4 hoursthen reading the absorbance on a plate reader. Solid samples were testedby 1) soaking polymers overnight in culture medium and the next dayremoving this medium and using it to set up cells in a new TC plate, tolook for toxic leachables from the samples and 2) seeding cells directlyonto the polymer samples. Cells were tested for cytotoxicity after 24 has described above.

In all cases, culture medium containing serum was used.

Results were recorded as % Attachment, calculated by result ofsample/result of negative cytotoxic control and expressed as apercentage. Results are summarized in Table 1 TABLE 1 Prepolymercytotoxicity results % Cell attachment Prepolymer Human stem HumanExamples cells Chondrocytes Example 1 80 80 Example 2 70 Example 3 60100 Example 24 100 100 Example 10 100 100 Control 100 100

TABLE 2 Polymer cytotoxicity results % Cell attachment Polymer Humanexamples stem cells Rat stem cells Example 11 100 95 Example 19 80Example 12 90 — Example 14 100 95 Example 17 70 95 Control 100 100 

Example 26

The in-vitro degradation under hydrolytic and oxidative environmentswere assessed according to procedures described in Biomaterials Vol. 17,No. 22, 2127, 1996 and Journal of Biomedical Material Research 29,467-475, 1995, respectively. Following is a brief description of theprocedures used.

Polymers prepared in Examples 11, 13, 14, 17, 22, and 23 were used inthis study.

Hydrolytic degradation: Three porous cylinder specimens of (6 D×12 mm H)(n=3) were placed in a perforated Teflon cage and placed inside a 500 mLSchott bottle containing approximately 400 mL buffered saline solution.Phosphate buffered saline solution of pH 7.4 was used. Schott bottleswere stored at 70° C. in an oven and solution pH measurements were takenat different time intervals. pH change in a control solution (withoutpolymer samples) was also measured. Specimens were removed from thebuffer and washed with deionised water thoroughly and dried undernitrogen atmosphere for 24 h at 40° C. followed by drying under vacuum(0.1 torr) for 48 h at 40° C. The dry weight was recorded and comparedwith their initial weight and total weight loss was measured.

Oxidative degradation: Three porous cylindrical test specimens (6 D×12 Hmm) (n=3) were placed in a perforated Teflon cage and immersed in 400 mlof hydrogen peroxide solution (30% w/v) containing 0.1 molar COCl₂ (pH3.69) in Schott bottle. Schott bottles were placed in an oven at 70° C.and pH measured at different time intervals. Peroxide solution wasreplaced with fresh solution after seven days. Change in pH in a controlsolution (no test specimens) was also measured. Specimens were removedfrom the peroxide solution and washed with deionised water thoroughlyand dried under nitrogen atmosphere for 24 h at 40° C. followed bydrying under vacuum (0.1 torr) for 48 h at 40° C. The dry weight wasrecorded and compared with their initial weight and total wt lossmeasured.

PBS buffer solution/pH 7.4/70° C. (1 month) and Oxidative environmentCOCl₂/H₂O_(2/)pH/3.69/70° C. (15 days) TABLE 3 Weight loss due tohydrolytic and oxidative degradation Wt Loss % in PBS Wt loss % in CoCl₂(hydrolytic degradation) (oxidative degradation) Polymer Examples Onemonth 15 Days Example 11  7  55 Example 17 12 100 Example 13 23 100Example 14 —  16 Example 22 49 — Example 23 22 —

Example 27

Materials: Prepolymer of MLDI and D-Glucose was prepared according toExample 3. Polycaprolactone triol (MW 300, PCLT-300, Aldrich) was driedby heating under vacuum (0.1 torr) at 90° C. for three hours and sodiumchloride (+80 mesh) (Aldrich) was used a received.

Degassed prepolymer (1.85 g) prepared in Example 3 was weighed in to acavity (20×20×10 mm) made in a Teflon block. Degassed and driedpolycaprolactone triol (MW 300, 0.74 g) was added to this prepolymerfollowed by 1.77 g of NaCl of approx. mesh size 80. The mixture wasmanually stirred for few seconds and then stannous 2-ethyl hexanoatecatalyst (0.0026, 0.1%) was added and stirred for few minutes. Thisprepolymer mixture remained a viscous liquid and was taken into a 2.5 mlsyringe and dispensed 0.29 g to each of the cylindrical (6 D×12 H mmsize) cavities in a Teflon mould and cured overnight at 38° C. The curedpolymer was then placed in large excess of deionised water. SEMmicrograph showed porosity between 200 and 300 microns.

Example 28

Materials: Prepolymer of MLDI and D-Glucose was prepared according toExample 3. Polycaprolactone triol (MW 300, PCLT-300, Aldrich) was driedby heating under vacuum (0.1 torr) at 90° C. for three hours and L-ysine(Aldrich) was used as received.

Degassed prepolymer (1.6 g) prepared in Example 3 was weighed in to acavity (20×20×10 mm) made in a Teflon block. Degassed and driedpolycaprolactone triol (MW 300, 0.51 g) was added to this prepolymerfollowed by L-Llysine (0.047 g) and water (0.006 g). The mixture wasstirred for few seconds and then stannous 2-ethyl hexanoate catalyst(0.002, 0.1%) was added and stirred further for 5 min. This prepolymermixture remained a viscous liquid and was taken into a 2.5 mL syringeand dispensed 0.29 g to each of the cylindrical (6 D×12H mm size)cavities in a Teflon mould and cured overnight at 38° C. to give porouscylindrical test specimens. The cured polymer samples were tested usingInstron (Model 5568 for compressive strength and modulus according toASTM method F451-95

The average compressive strength and modulus were 26.5±5 MPa and 707±91MPa, respectively.

Example 29

Materials: Prepolymer of MLDI and D-Glucose was prepared according toExample 9. Polycaprolactone triol (MW 300, PCLT-300, Aldrich) was driedby heating under vacuum (0.1 torr) at 90° C. for three hours.

Degassed prepolymer (1.38 g) prepared in Example 3 was weighed in to acavity (20×20×10 mm) made in a Teflon block. Degassed and driedpolycaprolactone triol (MW 300, 0.50 g) was added to this prepolymerfollowed by water (0.005 g). The mixture was stirred for 5 min. Thisprepolymer mixture remained a viscous liquid and was taken into a 2.5 mLsyringe and dispensed 0.29 g to each of the cylindrical (6 D×12H mmsize) cavities in a Teflon mould and cured 72 h at 38° C. to give porouscylindrical test specimens. The cured polymer samples were tested usingInstron (Model 5568) for compressive strength and modulus according toASTM method F451-95.

The average compressive strength and modulus were 30±4 MPa and 521±199MPa, respectively.

Example 30

Materials: Prepolymer of MLDI and Pentaerythritol tetrakis(3-mercaptopropionate) (PETPM) was prepared according to Example 10.Polycaprolactone triol (MW 300, PCLT-300, Aldrich) was dried by heatingunder vacuum (0.1 torr) at 90° C. for three hours.

Degassed prepolymer (1.81 g) prepared in Example 10 was weighed in to acavity (20×20×10 mm) made in a Teflon block. Degassed and driedpolycaprolactone triol (MW 300, 0.48 g) was added to this prepolymerfollowed by water (0.0048 g). The mixture was manually stirred for fewseconds and then stannous 2-ethyl hexanoate catalyst (0.0023, 0.1%) wasadded and stirred for 5 min. This prepolymer mixture remained a viscousliquid and was taken into a 2.5 mL syringe and dispensed 0.29 g to eachof the cylindrical (6 D×12 H mm size) cavities in a Teflon mould andcured overnight at 38° C. to give porous cylindrical test specimens. Thecured polymer samples were tested using Instron (Model 5568) forcompressive strength and modulus according to ASTM method F451-95.

The average compressive strength and modulus were 20.2±3 MPa and 507±156MPa, respectively.

Example 31

This example illustrates that human mesenchymal (bone marrow) stem cellscan be incorporated with the injectable biodegradable, biocompatiblepolyurethane/urea compositions of this invention and cured to from solidporous scaffolds without compromising cell viability. In addition cellculture of these plugs show that the stem cells can form new tissuematrix and with appropriate medium can differentiate intoosteoblast-like cells.

The injectable polymer system used in this experiment was based onprepolymer prepared according to Example 1, and polycaprolactone triol(MW 300) dried as described in Example 11.

Hollow fibres were precoated with fibronectin (10 μg/ml) at room tempfor 2 hrs before seeding with cells (2×10⁶ cells in 500 μl filled 2cartridges). Cartridges containing fibres were then placed in 10 cmdishes containing culture media (M199)+10% FCS. Medium was changed twiceweekly for 1 week. Cartridges were dismantled, and the fibres were cutinto approx 1 mm segments. The cell-seeded hollow fibre tubes werebisected and mixed with the polymer composition described in Example 11,then injected into a rubber tube and allowed to cure for 4 hrs. Thepolymer plugs containing the cell/hollow fibres were removed from thetube, cut in half and placed into 24 well tissue culture plates. Onehalf of the plug was maintained in standard medium M199 +10% FCS, theother half was further supplemented with differentiation mediumcontaining β-glycerol phosphate (1.5 mg/ml), dexamethasone (40 ng/ml)and ascorbate (20 μg/ml) to promote osteoblast differentiation. Cultureswere maintained for up to 6 weeks with medium changes every 2-3 days.The polymer plugs were harvested at 6 weeks and samples were processedand stained with standard haematoxylin & eosin, light green, Schiff'sreagent, as well as with von Kossa reagent for detection of bonemineralisation.

These experiments revealed the presence of both differentiated(osteoblast-like) and undifferentiated stem cells in the fibre/polymercomposite after culture. The differentiated cells showed the presence ofbone mineral as evidence by the brown/black Von Kossa staining. Theseresults provide evidence that the cells survive the polymer curingprocess and can differentiate producing bone mineral.

Example 32

This example illustrates that human chondrocytes can be incorporatedwith the injectable biodegradable, biocompatible polyurethane/ureacompositions of this invention and cured to from solid porous scaffoldswithout compromising cell viability. In addition cell culture of theseplugs show that chondrocytes form new tissue matrix.

The injectable biodegradable, biocompatible polyurethane/ureacomposition used in this experiment was based on prepolymer preparedaccording to example 3 and polycaprolactone triol (MW 300).

Human chondrocytes were isolated from fresh cartilage tissue accordingto Example 1 of PCT WO 02/062357 A1. Fresh cartilage tissue is collectedin DMEM/10% FBS or autologous serum containing 100 μg/ml penicillin andstreptomycin. After weighing, the tissue is placed in a sterile petridish containing 3-4 mL of DMEM and dissected into 1 mm³ pieces using asharp sterile scalpel. It is then digested with 10% w/v trypsin in PBSat 37° C. for 1 hour. Approximately 2 mL of 10% w/v trypsin is used pergram of tissue. The residual tissue pieces are collected bycentrifugation (1000 rpm, 5 mins) and washed with PBS, then water (usingapproximately 5-10 ml per gram of tissue). A second digestion step isthen performed overnight at 37° C. using 2 ml of a mixture of bacterialcollagenase and hyaluronidase per gram of tissue. The digestion mixtureis prepared by adding 2 mg hyaluronidase (1520 units) and 200 μl ofcollagenase stock (taken from a 3000 unit/ml stock, stored at −70° C. ina buffer of 50 mM tris, 10 mM CaCl₂, pH 7.0) to 2 ml of DMEM and filtersterilising. The digested tissue is passed through a 70 μm Nylon cellstrainer and the cells are washed and collected by centrifugation. Cellnumbers and viability are assessed using a trypan blue count on a smallknown aliquot.

Gelatin beads were prepared according to Example 7 of PCT WO 02/062357A1. Gelatin microparticles are synthesized by using emulsion method.Briefly, gelatin is dissolved in 50 mM acetic acid to 20% (w/v). Twohundred milliliters olive oil is warmed up to 37° C. The warmed oliveoil is stirred at 300 rpm. Forty millilitres gelatin solution kept at37° C. is then applied to olive oil through a 20-gauge needle. Thissolution is also prepared containing 10% w/w native collagen. Theemulsion is kept stirred for 90 minutes. The emulsion is then cooleddown by stirring at 4° C. for 30 minutes in order to harden the gelatinparticles. Five hundred millilitres of 0.2% Triton X-100 in PBS is addedto the emulsion and stirred at room temperature for 10 minutes. Themixture is then put in a separating funnel and settled for one hour. Theliquid in the lower potion is collected and after gelatin microparticlesprecipitate, the upper liquid decanted off carefully and the particlesrinsed with water two times. Five hundred millilitres of 0.1%glutaraldehyde in PBS is added to the gelatin microparticles and stirredfor one hour for cross-linking. The cross-linked gelatin beads are thenrinsed with water several times and soaked in ethanol. The ethanol isdecanted and the gelatin microparticles dried under vacuum. Beforeseeding cells, the gelatin beads are rehydrated with PBS overnight andthen with chondrocyte medium. The average size of gelatin microparticlesis about 110 μm.

Isolated chondrocytes were seeded on gelatin beads according to Example8 of PCT WO 02/062357 A1. Gelatin beads, providing a surface area of250-500 cm², are pre-washed with 50 mL of warmed media (DMEM/10% FBS orautologous serum containing 100 μg/ml penicillin and streptomycin) at37° C. then placed inside a 125 ml spinner bottle. 1×10⁵ cells, eitherfreshly isolated cells, previously passaged cells or previously isolatedand frozen cells, are added to the beads or particles. The bottle isthen stirred in a 37° C. incubator (with 5% CO₂), at 25 rpmintermittently for 2 minutes every 30 minutes for 3 hours, then 45 rpmintermittently for 2 minutes every 30 minutes for the next 3 hours, thencontinuously first at 45 rpm for 15 minutes, then 50 rpm for 15 minutes,55 rpm for 15 minutes, then to the final speed of 60 rpm. The cells arethen grown at this speed until 90% confluence is achieved, usually 5-8days depending on the original inoculum.

For collection of the cells 6 mL of warm 0.3% w/v trypsin is addeddirectly to the washed cells on beads and incubated at 37° C. for 20minutes. The gelatin beads were digested by the enzyme, releasing thecells into solution without the need for extensive mechanical agitation.Cells were collected by centrifugation at 1000 rpm for 5 mins. Removethe supernatant and gently resuspend the cells in 5 mL of media. Cellsare counted using a trypan blue method and re-seeded onto fresh 0.025%cross-linked gelatin beads as previously described at various celldensities for mixture with synthetic delivery polymers.

Prepolymer prepared according to Example 3 (1.00 g) and polycaprolactonetriol (MW 300) (0.402 g) were weighed separately into 1 mL syringes andsterilized by gamma radiation (25 KG). Prepolymers in syringes werecompletely emptied into sterile pots and mixed at ambient temperaturefor three minutes. The mixture was allowed to stand at ambienttemperature in the biohazard safety cabinet. The polymer mixture wasallowed to cure for varying times (14 to 80 minutes) in pots until theviscosity began to increase sufficiently to indicate significant curinghad occurred. In the example shown the viscosity increased at 63minutes. Harvested cells on gelatines beads were centrifuged to minimisethe amount of medium and then added. Cells/beads (0.25 ml) and polymerwere mixed for 1 minute to give a 15% bead/cells to polymer mixtureratio. The total mixture of cell/beads and polymer were transferred asviscous drips into 24 well tissue culture containers. Curing was allowedto continue for a further 2 hrs and 25 minutes to form solid plugs.Culture medium (DMEM/10% FCS) was added and plugs were cultured andexamined at various times points ranging from 6 days to 9 weeks. Mediumwas changed every 2-3 day and samples of tissue plugs were harvested forstandard haematoxylin & eosin staining and alcian blue staining.

These experiments demonstrated that human chondrocytes grown and seededonto beads (gelatin) survive the polymer curing process and can furtherproduce new matrix.

Example 33

Materials: Pentaerythritol (Aldrich) was dried overnight in a vacuumoven (0.1 torr) at 80° C. MLDI and 1,4-diazabicyclo[2.2.2]octane (DABCO8154, Air Products & Chemicals Inc) were used as received.

Predried pentaerythritol (5.0 g) was weighed in to a dry three-neckround bottom flask equipped with a magnetic stirrer, nitrogen inlet anddrying tube. Methyl 2,6-diisocynato hexanoate (MLDI) (31.17 g) was thenweighed and added to the flask followed by DABCO 8154 Catalyst (0.1 wt%). The reaction mixture was stirred and heated at 50° C. for 4 d undernitrogen atmosphere. The homogenous polymer mixture was then degassedunder vacuum (0.1 torr) at the above temperature, transferred to a vialunder nitrogen atmosphere and stored in the refrigerator. The prepolymerwas analysed by GPC and Rheometer (CSR-10) using methods described inExample 1.

The prepolymer number average molecular weight was 1579 and thepolydispersity was 1.66. Instantaneous viscosity was 10×10⁵ cSt at 23°C.

Example 34

This example illustrates that porous polymers prepared according to thisinvention are biocompatible. The biocompatibility was evaluated byimplanting porous polymer test specimens in Rats for two months.

The porous polymers used in the implant study were prepared by mixingprepolymer A with Component B and the details of various compositionsare shown in Table 4. Porous polymer cylinders. TABLE 4 Composition ofpolymers used in the rat implant study Prepolymer A (quantity ComponentB (quantity Implant Sample # g) g) 1 Example 3 (2.14) PCLT 300 (0.862) 2Example 3 (2.13) PCLT-300:DDAPS* (0.772:0.103) 3 Example 3 (1.36)PCLT-900 (1.64) 4 Example 5 (2.2) PCLT-300 (0.9) 5 Example 3 (2.0)PCLT-300:DPCLPC** (0.48:0.808) 6 Example 3 (2.0 g) PCLT-300:DPCLPC**(0.725:0.201)*DDAPS was prepared according to the procedure in Example 24**DPCLPC was prepared according to the procedure in Example 20

Cylindrical test specimens (6 D×10 H mm) were prepared using thefollowing procedure for all implant samples.

Degassed prepolymer was weighed in to a cavity (20×20×10 cm) made in aTeflon block. Degassed and dried prepolymer B was weighed and added tothe prepolymer A. The mixture was stirred for few seconds and thenstannous 2-ethyl hexanoate catalyst (0.25% of total mixture) was addedand stirred for 20 min. Gelatine beads (ave. size 100-200 micron, inwater, 0.1 mL per 1.0 g prepolymer mixture,) was added to this mixtureand stirred for about 1 minute. The viscous polymer was then taken intoa 2.5 mL syringe and dispensed 0.29 g into each cylindrical cavity (6 mmD×10 mm H) in a multi-cavity Teflon mould and cured overnight at 38° C.to give porous cylindrical polymer test specimens.

Implantation Procedure and results: The in vivo biocompatibility andbiodegradation of preformed polymers were conducted using standardmethods in female rats. The procedure is as follows: Eight week old,female, Sprague Dawley rats were anaesthetised using a ketamine/xylazinemixture. Once anaesthetised a subcutaneous pocket was created in theback of the rat. Two 6 mm D×10 mm H sterile preformed polymers wereinserted into the pocket, one to the left and the other to the right ofthe initial incision. Once in place the wound was closed with a 9 mmwound clip. Animals were monitored every 2 hrs for the first 6 hours andevery 12 hours for the first 3 days. Intensive monitoring was undertakenevery 2 weeks, which included weighing the animals, visual monitoring ofthe surgical site, and measuring of the polymers with digital callipers(length and width) to assess degradation.

At set time points the animals were killed with Nembutal (sodiumpentobarbitone), serum was collected, polymer with surrounding tissuewas excised. The polymer was fixed in formalin and processed forhistological analysis. All major organs prior to removal were assessedfor signs of gross pathology. Once removed, these organs were weighedand then pieces processed for histology.

After 2 and 4 months in vivo all rats showed no signs of disease, allgained weight similar to the controls and there was no swelling oradverse reactions to the presence of the polymers. No gross pathologywas seen in any major organ. After 4 months a small soft capsule hadformed around the polymers. No calcification was noted. Analysis ofHaematoxylin and Eosin stained sections at 2 and 4 months revealed anormal looking dermis. Occasional neutrophils were noted however therepresence was due to mechanical shearing induced by some movement ofpolymer. At 2 months some polymers had fibroblast infiltration ofpolymer pores that were adjacent to the dermal tissue. This became morepronounced at 4 months. At 4 months the fibroblast infiltration hadprogressed further into the polymer than just on the edge. FIG. 18 showshistology images illustrating good tissue integration after two-monthimplantation.

Example 35

Materials: Prepolymer of MLDI and D-glucose was prepared according toExample 3. Polycaprolactone triol (MW 300, Aldrich) was dried by heatingunder vacuum (0.1 torr) at 90° C. for three hours and2-(2-aminoethylamino)ethanol (Aldrich) was used as received.

Degassed prepolymer (1.35 g) prepared in Example 3 was weighed in to acavity (20×20×10 mm) made in a Teflon block. Degassed and driedpolycaprolactone triol (0.438 g) and water (0.005 g) were added. Themixture was manually stirred for several minutes and then2-(2-aminoethylamino) ethanol (0.014 g) was added and stirred foradditional 1 min. This prepolymer mixture remained a viscous liquid andwas taken into a 2.5 mL syringe and dispensed 0.29 g to each of thecylindrical (6 mm D×12 mm H) cavities in a Teflon mould and curedovernight at 38° C. to give porous cylindrical test specimens. The curedpolymer samples were tested using Instron (Model 5568) according to ASTMmethod F451-95.

The average compressive strength and modulus were 18.4±4 MPa and 691±104MPa, respectively.

Example 36

Materials: Prepolymer of MLDI and D-glucose was prepared according toExample 3. Four-arm amine terminated PAMAM dendrimer (generation 0) waspurchased from Aldrich as a 20 wt. % solution in methyl alcohol. PAMAMin PBS buffer solution was prepared by evaporating methanol anddissolving to make a 20 mg/mL dendrimer in 0.0104 molar PBS buffersolution.

Degassed prepolymer (1.29 g) prepared in Example 3 was weighed in to acavity (20×20×10 mm) made in a Teflon block. A solution of PAMAMdendrimer in buffer solution (MW 516.68, 0.5 g) was added to thisprepolymer. The mixture was stirred for few seconds before taking into a2.5 ml syringe and dispensed 0.29 g to each of the cylindrical (6 D×12 Hmm size) cavities in a Teflon mould and cured overnight at 38° C. andgave solid, porous cylindrical test specimens.

Example 37

Materials: MLDI and titanium (IV) butoxide were used as received,whereas pentaerythritol (Aldrich) was dried as described in Example 1.

Predried pentaerythritol (2.0 g) was weighed into a dry three-neck roundbottom flask equipped with a magnetic stirrer, nitrogen inlet and dryingtube. Methyl 2,6-diisocynato hexanoate (MLDI) (12.46 g) was weighed andadded to the flask followed by titanium IV butoxide (0.014 g). Thereaction mixture was stirred and heated at 50° C. for 24 h undernitrogen atmosphere. The homogenous polymer mixture was then degassedunder vacuum (0.1 torr) and transferred to a vial under nitrogenatmosphere and stored in the refrigerator.

The prepolymer number average molecular weight was 1366 and thepolydispersity was 1.85. Instantaneous viscosity was 8.0×10⁴ cSt at 23°C.

Degassed prepolymer (1.62 g) prepared was weighed in to a cavity(20×20×10 mm) made in a Teflon block. Degassed and driedpolycaprolactone triol (MW 300, 0.595 g) was added to this prepolymerfollowed by water (0.005 g). The mixture was stirred for few seconds andthen catalyst titanium (IV) butoxide (0.002, 0.1%) was added andstirred. This prepolymer mixture remained a viscous liquid and was takeninto a 2.5 mL syringe and dispensed 0.29 g to each of the cylindrical (6mm D×12 mm H) cavities in a Teflon mould and cured overnight at 38° C.to give a porous cylindrical test specimens. The cured polymer samplesshowed compressive strength and modulus of 21.3±2.9 MPa and 678±57 MPa,respectively when tested using Instron (Model 5568) according to ASTMmethod F451-95.

Example 38

Materials: Linear polycaprolactone diol (MW400, Aldrich) was dried in avacuum oven (0.1 torr) at 80° C. for 3 h. MLDI and stannous 2-ethylhexanoate were used as received.

Predried polycaprolactone diol MW 400 (5.0 g) was weighed in to a drythree-neck round bottom flask equipped with a magnetic stirrer, nitrogeninlet and drying tube. Methyl 2,6-diisocynato hexanoate (MLDI) (5.3 g)was then added to the flask followed by 0.1 wt % stannous 2-ethylhexanoate catalyst. The reaction mixture was stirred and heated at 50°C. for 4 h under nitrogen atmosphere. The homogenous polymer mixture wasthen degassed under vacuum (0.1 torr) and stored in the refrigerator.The prepolymer was analysed by GPC and showed number average molecularweight 1970 and polydispersity 1.53.

Example 39

Materials: L-lysine (Aldrich), MLDI and stannous 2-ethyl hexanoate wereused as received.

L-lysine (2.03 g) was weighed in to a dry three-neck round bottom flaskequipped with a magnetic stirrer, nitrogen inlet and drying tube. Methyl2,6-diisocynato hexanoate (MLDI) (8.85 g) was added to the flaskfollowed by 0.1 wt % stannous 2-ethyl hexanoate catalyst. The reactionmixture was stirred and heated at 50° C. for 112 h under nitrogenatmosphere. The homogenous polymer mixture was then degassed undervacuum (0.1 torr) at the above temperature and stored in therefrigerator. The prepolymer was analysed by GPC and showed numberaverage molecular weight 620 and the polydispersity 1.25.

Example 40

Materials: Prepolymer of MLDI and DG-Glucose prepared according toExample 3. Polycaprolactone triol (MW 300, PCLT-300, Aldrich) was driedby heating under vacuum (0.1 torr) at 90° C. for three hours. PeptideJAMR.49 (Ac-GEKGPAGERGAXGPAGPRGPXGPXGPXGPXGV-OH (X=Hyp) was used asreceived (MW 2800).

Degassed prepolymer (1.52 g) prepared in Example 3 was weighed in to acavity (20×20×10 mm) made in a Teflon block. Degassed and driedpolycaprolactone triol (MW 300, 0.543 g) was added to this prepolymerfollowed by the peptide (0.205 g) and water (0.005 g). The mixture wasmanually stirred for several minutes and then stannous 2-ethyl hexanoatecatalyst (0.002, 0.1%) was added and stirred. This prepolymer mixtureremained a viscous liquid and was taken into a 2.5 ml syringe anddispensed 0.29 g to each of the cylindrical (6 mm D×12 mm H) cavities ina Teflon mould and cured overnight at 38° C. to give a porouscylindrical test specimens. The cured polymer samples were tested usingInstron (Model 5568) according to ASTM method F451-95 and exhibited14.2±6.9 MPa compressive strength and 517±195 MPa compressive modulus.

It will be appreciated that the invention is not limited to the coremolecules, isocyanates, or functional oligomers and degradable arms asset out hereinabove. Rather the limits of this invention will beappreciated by the functional need to deliver a preferably injectableand flowable prepolymer composition for in vivo or ex vivo low exothermcuring with a functional oligomer so as to form as polymeric, optionallyliving scaffold. In particular, however, an injectable biodegradable,biocompatible polyurethane/urea composition must meet the followingrequirements to be useful in bone and cartilage applications. Ideallythe prepolymer should be in liquid/paste form, sterilizable withoutcausing any chemical change, and have the capacity to incorporatebiological matrix components. Upon injection the prepolymer mixtureshould bond to biological surface and cures to a solid and preferablyporous scaffold with appropriate mechanical properties to suit theapplication. The curing should be with minimal heat generation and thechemical reactions involved in curing should not damage the cells oradjacent tissues. The cured polymer while facilitating cell in-growth,proliferation and migration, should ideally be degraded to biocompatiblecomponents that are absorbed to the body or released from the body.

REFERENCES

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1. A star, dendrimer or hyper-branched flowable prepolymer compositioncomprising the reaction product of isocyanate and low molecular weightmultifunctional core molecules having at least two and preferably threeor more functional groups that react with said isocyanate to formurethane or urea groups.
 2. A prepolymer composition as claimed in claim1 wherein said low molecular weight multifunctional core molecule isselected form the group consisting of diols, triols, and polyols such assugar molecules.
 3. A prepolymer composition as claimed in claim 1,wherein said low molecular weight multifunctional core molecule has amolecular weight of 400 or less.
 4. A prepolymer composition as claimedin claim 1, wherein said isocyanate is optionally substituted aliphatic,aromatic and hindered isocyanate.
 5. A prepolymer composition as claimedin claim 1, wherein said isocyanate is aliphatic and asymmetric inmolecular shape.
 6. A prepolymer composition as claimed in claim 1wherein the viscosity of the prepolymer composition on preparation isabout 15,000-200,000 cSt at room temperature.
 7. A prepolymercomposition as claimed in claim 1, further comprising biological andinorganic components selected from the group consisting of cells,progenitor cells, growth factors, other components for supporting cellgrowth, calcium phosphate, hydroxyapatite, adhesives including fibrin,collagen and transglutaminase systems, surfactants including siloxanesurfactants, porogens including silica particles, powdered silica,sugars and sodium chloride type salts, polymeric hollow fibres andgelatin beads.
 8. A prepolymer composition as claimed in claim 1comprising the reaction product of pentaerythritol and methyl2,6-diisocyanato hexanoate.
 9. A prepolymer composition as claimed inclaim 1, comprising the reaction product of glucose and methyl2,6-diisocyanato hexanoate.
 10. A prepolymer composition as claimed inclaim 1, comprising the reaction product of glucose and ethyl2,6-diisocyanato hexanoate.
 11. A biodegradable biocompatiblepolyurethane/urea polymer composition comprising the reaction product ofa prepolymer of claim 1, and linear star dendrimer or hyperbranched softsegment forming functional oligomers with degradable arms.
 12. Abiodegradable biocompatible polyurethane/urea polymer composition asclaimed in claim 11 wherein said linear star dendrimer or hyperbranchedsoft segment forming functional oligomer with degradable arms isselected from the group consisting of lactides, glycolides,lactide/glycolides, caprolactones, propylene fumarates, glycolic acid,dioxanones, anhydrides, polyorthoesters and phosphorylcholines.
 13. Abiodegradable biocompatible polyurethane/urea polymer composition asclaimed in claim 11, wherein said linear star dendrimer or hyperbranchedsoft segment forming functional oligomer with degradable arms iszwitterionic.
 14. A biodegradable biocompatible polyurethane/ureapolymer composition as claimed in claim 11, comprising the reactionproduct of water, polycaprolactone triol and a prepolymer comprising thereaction product of pentaerythritol and methyl 2,6-diisocyanatohexanoate.
 15. A biodegradable biocompatible polyurethane/urea polymercomposition as claimed in claim 11, comprising the reaction product ofwater, polycaprolactone triol and a prepolymer comprising the reactionproduct of glucose and methyl 2,6-diisocyanato hexanoate.
 16. Abiodegradable biocompatible polyurethane/urea polymer composition asclaimed in claim 11, comprising the reaction product of water andpolycaprolactone triol and a prepolymer comprising the reaction productof glucose and ethyl 2,6-diisocyanato hexanoate.
 17. A biodegradablebiocompatible polyurethane/urea polymer composition as claimed in claim11, comprising the reaction product of polycaprolactone triol anddihydroxypolycaprolactone phosphoryl choline and a prepolymer comprisingthe reaction product of pentaerythritol and methyl 2,6-diisocyanatohexanoate.
 18. A biodegradable biocompatible polyurethane/urea polymercomposition as claimed in claim 11, comprising the reaction product ofpolycaprolactone triol and a 1,2-dihydroxy-N,N-dimethylaminopropanesulfonate zwitterion and a prepolymer comprising the reaction product ofglucose and methyl 2,6-diisocyanato hexanoate.
 19. A biodegradable,biocompatible polymeric scaffold comprising a cured biocompatible,biodegradable polyurethane/urea composition as claimed in claim
 14. 20.A biodegradable, biocompatible polymeric scaffold as claimed in claim 19having a compressive strength in the range of 0.05-80 MPa.
 21. Abiodegradable, biocompatible polymeric scaffold as claimed in claim 19,having pores in a size range of 150-300 micron.
 22. A biodegradable,biocompatible polymeric scaffold as claimed in claim 14, furthercomprising biological components selected from the group consisting ofcells, progenitor cells, growth factors, other components for supportingcell growth, calcium phosphate, hydroxyapatite, adhesives includingfibrin, collagen and transglutaminase systems, surfactants includingsiloxane surfactants, porogens including silica particles, powderedsilica, sugars, sodium chloride type salts, polymeric hollow fibres andgelatin beads
 23. A process for the preparation of a biocompatible,biodegradable polyurethane/urea composition as claimed in claim 11comprising reacting an isocyanate with a core molecule having at leasttwo and preferably three or more functional groups that react with saidisocyanate to form urethane or urea groups under suitable conditions toform a prepolymer composition with a flowable viscosity; and reactingsaid prepolymer with a star soft segment forming functional oligomerwith degradable arms and optionally, appropriate amounts of water andcatalyst under conditions such that the reaction temperature does notexceed 90° C.
 24. A process as claimed in claimed in claim 23 whereinthe functional oligomer is soluble in said prepolymer.
 25. A process asclaimed in claim 23, further comprising the step of reacting saidprepolymer with high molecular weight degradable polymer selected fromthe group consisting of PLGA, PLLA and poly(anhydrides).
 26. Abiodegradable, biocompatible polyurethane/urea scaffold prepared byreacting an isocyanate with a core molecule having at least two andpreferably three or more functional groups that react with saidisocyanate to form urethane or urea groups under suitable conditions toform a flowable prepolymer; and reacting said prepolymer with a starsoft segment forming functional oligomers with degradable arms andoptionally, appropriate amounts of water and catalyst under conditionssuch that the reaction temperature does not exceed 90° C.
 27. A methodof treatment of damaged bone or cartilage in a patient requiring suchtreatment, the method comprising administering to said patient abiocompatible, biodegradable polyurethane/urea composition as claimed inclaim 11, said administration occurring by the implant of a scaffoldformed ex-vivo from a cured form of said polyurethane/urea composition,or by the injection of said polymer in an uncured form for in-vivocuring and scaffold formation.
 28. A process of repairing bone and/orcartilage comprising integrating said scaffold formed from saidbiocompatible, biodegradable polyurethane/urea composition as claimed inclaim 11 with bone and/or cartilage.
 29. The process for the preparationof a biocompatible, biodegradable polyurethane/urea composition asclaimed in claim 23, wherein the reaction temperature does not exceed60° C.
 30. The process for the preparation of a biocompatible,biodegradable polyurethane/urea composition as claimed in claim 29,wherein the reaction temperature does not exceed 40° C.
 31. Thebiodegradable, biocompatible polyurethane/urea scaffold as claimed inclaim 26, wherein the reaction temperature does not exceed 60° C. 32.The biodegradable, biocompatible polyurethane/urea scaffold as claimedin claim 31 wherein the reaction temperature does not exceed 40° C.